This invention relates to managing assets equipped with active electronic tags.
Asset management systems attempt to monitor the existence, location and status of items being transported or stored. The systems include two main types: barrier systems and continuous systems.
Barrier systems determine whether an asset is located within a cell delimited by a set of stationary interrogators. The interrogators detect the asset as it crosses a boundary of the cell, but are incapable of determining a position of the asset within the cell.
Typical barrier systems fix a bar code to each asset, and use bar code readers as interrogators. Examples include systems used by car factories and mail carriers, such as Federal Express and United Parcel Service.
Another type of barrier system attaches a transponder to each asset and uses radio transceivers as interrogators. The transponders are passive, that is, they respond when activated by an interrogator but are incapable of initiating communications or other functions. An example includes a railroad system developed by AMTECH, in which each railroad car on a train is equipped with a transponder. Interrogators include transceivers that are placed along a railway.
Continuous systems determine the position of an asset anywhere within a monitoring area. An example, implemented by LOJACK, equips cars with an active transponder. The transponder is active because it initiates its own functions, for example, it monitors a particular hailing frequency. If the car is stolen, LOJACK uses special transmitters to establish communication with the transponder at the hailing frequency. Receivers provided to police cars analyze the communications to locate the car.